Multidimensional memory topography in the medial parietal cortex identified from neuroimaging of thousands of daily memory videos

Our memories form a tapestry of events, people, and places, woven across the decades of our lives. However, research has often been limited in assessing the nature of episodic memory by using artificial stimuli and short time scales. The explosion of social media enables new ways to examine the neural representations of naturalistic episodic memories, for features like the memory’s age, location, memory strength, and emotions. We recruited 23 users of a video diary app (“1 s Everyday”), who had recorded 9266 daily memory videos spanning up to 7 years. During a 3 T fMRI scan, participants viewed 300 of their memory videos intermixed with 300 from another individual. We find that memory features are tightly interrelated, highlighting the need to test them in conjunction, and discover a multidimensional topography in medial parietal cortex, with subregions sensitive to a memory’s age, strength, and the familiarity of the people and places involved.


Table of Contents
. Comparisons of memory properties and ROI signal by hemisphere 8 Supplemental Table 2. Comparisons of memory properties in a combined model and ROI signal 9 Supplemental Table 3  Shown are results from simple linear regressions quantifying the relationship of a given memory property (age, memory strength, emotion, and distance) and mean beta value, across voxels in anatomically-defined ROIs within the medial temporal lobe. Indicated are the beta-value () from the regression, and the p-value resulting from the two-sided t-test comparing the beta values across participants with a null hypothesis of 0 slope. Regressions with p < 0.05 are colored in grey. Age is measured as number of days from the scan; memory strength is from 1 (very weak) to 5 (very strong); emotion is from 1 (very negative) to 5 (very positive); and distance is number of km from the scanning center. (Hipp = hippocampus, Amyg = amygdala, ERC = entorhinal cortex, PHC = parahippocampal cortex.)  Figure 5. Alternate views of memory content representations. These maps show alternate viewpoints of the results shown in Figure 6. Specifically, these maps show whole-brain results from a multiple regression predicting voxel beta values from separate predictors for a memory's distance, age, strength, and emotion. Activation represents the mean regressor slope (β) for each predictor, where significance was assessed by comparing the slope across all participants with a two-sided t-test versus a null hypothesis slope of 0 (p < 0.01, uncorrected  Figure 6. Representations of different memory content, at stringent thresholds. Shown are bilateral maps of the data shown in Figure 6 and Supplemental Figure 5 at more stringent thresholds. These maps show the results from a multiple regression predicting voxel beta values using predictors for a memory's distance, age, strength and emotion (testing beta values with a two-sided t-test versus 0). The colormaps represent the range of beta values for each predictor, after centering. Memory strength and emotion maps are thresholded here at an FDR-corrected threshold of q < 0.01. For memory age, no voxels were significant after FDR correction; the above map shows an alternate threshold of p < 0.001 uncorrected. No significant voxels emerged for memory distance at either threshold.

Mem. Age
(p < 0.001; no sig. voxels at q < 0.05)  Figure 6, for predicting voxel beta values from separate predictors for a memory's distance, age, strength, and emotion. Activation represents the mean regressor slope (β) for each predictor, where significance was assessed by comparing the slope across all participants with a two-sided t-test versus a null hypothesis slope of 0 (p < 0.01, uncorrected). The colormaps represent the range of beta values for each predictor, after centering. However, in contrast with Figure 6 which used all memory videos, this regression was only conducted with memory videos that occurred within 50km of the scan center, to more closely approximate the short distances used in prior autobiographical memory neuroimaging work 2 . 50km was chosen as the optimal distance to cover the broader Washington DC metropolitan area where participants resided, including Northern Virginia and Baltimore. However, this cut-off does eliminate over one-third of the videos recorded in the study (M=111.9 videos, SD=86.4 per participant occurred over 50km away), so statistical power is likely much lower. In these surface maps, the same regions emerge for memory age, memory strength, and emotion as seen when using all memories (Figure 6), such as distinct medial parietal areas sensitive to temporally remote memories and strong memories. New regions emerge sensitive to memory distance along the temporal lobe. However, we find no regions sensitive to distance in the medial parietal cortex, and the temporal regions show no overlap with our anatomically defined medial temporal lobe areas, such as the hippocampus or parahippocampal cortex. Supplemental Figure 8. Map of memory content representations, with regressors included for people and place familiarity. These maps show a multiple regression (similar to that in Figure 6), using all memory videos, for predicting voxel beta values from separate predictors for a memory's distance, age, strength, emotion, people familiarity, and place familiarity. People and place familiarity were modeled categorically. Activation represents the mean regressor slope (β) for each predictor, where significance was assessed by comparing the slope across all participants with a two-sided t-test versus a null hypothesis slope of 0. Given the exploratory nature of this regression, maps are shown at a liberal threshold (p<0.05, uncorrected). The colormaps represent the range of beta values for each predictor, after centering. Similar regions emerge for memory age, strength, and emotion as in the original regression (Figure 6) Supplemental Figure 9. Whole-brain views of the memory topography. These maps show the same information in Figure 8, but across the whole brain. Shown are the top 1000 voxels across the cortex with signal for four different types of information: people familiarity, memory strength, memory age, and place familiarity. Each map is shown at 50% transparency; if a voxel is shared across multiple content types, it will be colored by both maps. While the medial parietal lobe shows the densest distribution of all four types of information with distinct voxel clusters, overlapping regions for people familiarity and memory strength are present in lateral occipital regions. Age, memory strength, and people familiarity also show overlapping sensitivity in orbitofrontal regions.

Memory Topography
Medial Lateral Ventral memory strength memory age people familiarity place familiarity Supplemental Figure 10. Whole-brain views of the memory topography on the same colormap. These maps show the same data as in Supplemental Figure 9 (the top 1000 voxels for each memory information type), but each information type is on its own brain, and all maps are using the same colormap, representing the range of beta values from -20.00 to 20.00.
Place Fam.
Supplemental Figure 11. Whole-brain views of the top voxels for emotion. Shown are the top 1000 voxels across the cortex with signal for emotion information in a memory. The colormap shows the range of beta values, on the same range as Supplemental Figure 10. While these peaks for emotion occur in early visual cortex, subcortical areas, and frontal cortex, no voxels appear in the medial parietal cortex.